This project is an investigation of the role of prostaglandins in cardiac regulation of coronary flow (autoregulation, local regulation). A constituent of blood plasma stimulates prostaglandin synthesis, causes coronary vasoconstriction, and augments regulation of coronary flow in isolated rabbit hearts. This investigation is concerned with (1) whether or not cardiac prostaglandin synthesis is an incidental event or plays an integral role in regulation of coronary flow, (2) the causal relationships between plasma-stimulated prostaglandin synthesis and plasma-induced coronary vasoconstriction, (3) the relationship between plasma-induced vasoconstriction and plasma-augmented autoregulation. The effects of the active plasma constituents, and its interaction with inhibitors of prostaglandin synthetase, will be examined in isolated hearts and in preparations of prostaglandin synthetase. The effect of the active plasma constituent on the ability of isolated hearts to regulate coronary flow in response to various stimuli (e.g., changes in perfusion pressure or perfusate oxygen concentrations) will be determined. BIBLIOGRAPHIC REFERENCE: Moretti, R.L., S. Abraham and R.R. Ecker, The stimulation of cardiac prostaglandin production by blood plasma and its relationship to the regulation of coronary flow in isolated isovolumic rabbit hearts, Circ. Res. 39:231-238, 176.